Nixie frequency counter gone timepiece

[Windell] of Evil Mad Scientist Laboratories took an ancient Nixie tube based frequency counter and converted it into a clock. The unit he got his hands on is an HP model that was still in great shape. He’s using an internally generated one second pulse as the clock signal, but some modifications are necessary to display time. That’s because the frequency counter is base 10 and clocks use a quirky combination of base 60 and base 12.

It wasn’t too much of a problem to rig up a system to track minutes and seconds. The tens digit for each is monitored by a couple of AND gates that he added to the mix. When they detect a ‘6’ the digit is reset and a pulse increments the next digit as the carry. This is more difficult to accomplish with the hours though. Minutes and seconds count from 0 to 59 but hours don’t start at 0. Instead of over-complicating the logic [Windell] used a bit of slight-of-hand. The Nixie tubes for the hours have been rewired so that when the counter is at 0, the filament in the shape of a 1 lights up. No difference in logic, just a translation that makes them display one digit higher than the actual count.

Projects like this are great for people who want to make a nixie clock but aren’t comfortable messing with high-voltage power supplies. I turned a busted one into a clock last year and it’s still on my desk, ticking away.

Wasn’t there some guy who turned an unmodified frequency counter into a clock by feeding it exactly the right amount of high-speed pulses to make the display show the time? I think I saw that a couple years ago but I don’t have a link. Ingenious idea though.

@matt: I believe that was also a work of cleverness. Any time there was a rollover, the entire counter was reset and clocked back to the correct ‘time’ value, but so fast that POV takes over and you only see one update.

I think that’s how it went anyway. Can’t remember what the update time was like though.

@matt You don’t need a HV supply, just a driver chip like the 7441 or similar solution. You will still have HV on your board, but it is very low current.

Is there a site for buy/sell/trade used instruments? I would love to get a decent 4 channel oscilloscope. All I can find is either high quality calibrated used equipment that costs $$$$ or old phosphor scopes…

@Squirrel, zool, s
I’d love a good trade/loan system or forum. I’ve got some equipment that I’ve picked up and only used for one or two projects but otherwise sits on a shelf. I grabbed a good 1980’s HP 1630 series logic analyzer that I used for one project and now it sits waiting for another purpose.

I hate that all of this great old test equipment is getting turned into clocks. Vintage oscilloscopes, frequency counters, and voltmeters are fun to use and much more expensive/rare than clocks.

It might have been neat if he had built something he could plug into the frequency counter which would generate frequencies that could display the time. I wouldn’t have been that much more difficult, it wouldn’t have destroyed the frequency counter, and it would have been portable to every other frequency counter ever made. Someone needs to do that.